This invention relates to a magnetically driven pump of the type in which an impeller is rotatively driven by magnetic force. The pump is capable of being used in a water pump or the like in a water cooling system of an internal combustion engine for an automotive vehicle.
A water jacket is formed in a vehicle engine in order to cool the engine, and a water pump is connected to the water jacket. The water pump has a pump chamber that communicates with the water jacket, and an impeller is supported within the pump chamber so as to be capable of rotating about its axis.
A water pump disclosed in Japanese Utility Model Laid-Open Publication No. Sho 60-159899(1985) includes a driven permanent magnet secured to an impeller at the position of its central axis. A drive shaft having a driving permanent magnet in parallel with its central axis is employed as a drive unit in a crank chamber, which is partitioned from the pump chamber by a partitioning plate. The driven permanent magnet of the impeller and the driving permanent magnet of the drive shaft constitute magnetic attraction means for rotatively driving the impeller by their magnetic forces.
Further, Japanese Patent Laid-Open Publication No. Sho 63-189690(1988) discloses a pump having a permanent-magnet rotor formed as an integral part of an impeller in a pump chamber, and a solenoid-type stator serving as a drive unit secured in a stator chamber partitioned from the pump chamber. The permanent-magnet rotor forming part of the impeller and the solenoid-type stator serve as magnetic attraction means and construct a motor.
In these conventional magnetically driven pumps, the magnetic force of the magnetic attraction means formed by the driving permanent magnet of the drive shaft provided in parallel with the central axis or by the solenoid-type stator influences, from one direction, the magnetic attraction means formed by the driven permanent magnet of the impeller or by the permanent-magnet rotor of the impeller, wherein these magnetic attraction means are provided in parallel with the central axis. As a result, the impeller is driven into rotation and produces a circulatory flow inside the pump chamber. By partitioning the pump chamber retaining the impeller from the crank chamber or stator chamber holding the drive shaft or solenoid-type stator, the drive unit is provided outside the pump chamber. Consequently, in comparison with an ordinary pump in which the pump chamber and crank chamber are sealed by mechanical seals, it is possible to prevent noise and leakage of fluid from the mechanical seals. Another advantage is their simpler structure.
However, a shortcoming of these conventional magnetically driven pumps is that since the magnetic attraction means are provided in parallel with the central axis, the mutual magnetic force is inadequate. As a consequence, the impeller cannot follow up sudden fluctuations in rotational speed and it is difficult to rotate the impeller at high speed. If such a pump is used to cool an engine, the result is a loss in the circulation of fluid and a decrease in circulatory flow rate. The end result is unsatisfactory cooling of the engine.
If both magnetic attraction means are elongated along the central axis with a view to rotating the impeller reliably at high speed, the result is a longer pump in the axial direction. This makes it more difficult to install the pump in a vehicle.